memory error when CTypedPtrArray<CPtrArray, ClassType*> element class has any virtual method

In VC++ 6.0 console application with linking MFC dll on windows 2000 server, if the element class of CTypedPtrArray has any virtual method(s), memory access error will occur under the following case: allocate a object of ClassType from heap with "new", add the pointer to this object onto CTypedPtrArray object, take and remove an element from the head of CTypedPtrArray, do sth (e.g. access its data) with the element, finally memory access error occurs while deleting the element.

The example  always has such a  memory access error regardless of relase/debug modes as long as the element class has any virtual methods. If we remove specifier 'virutal' before name of class methods, everything works fine in both debug and release modes.

struct PacketHeader
{
	unsigned long tag;		
	unsigned short msgid;	
	unsigned short status;	
	unsigned long timestamp;	
	char callerid[12];		
};
 
class CTaskObj
{
public:
	SOCKADDR_IN		cliAddr;
	// struct sockaddr_in	cliAddr;
	struct PacketHeader	msgHeader;
	char* pDataBuf;
	int		nBufSize;
 
public:
	CTaskObj();
//	 ~CTaskObj();
	virtual ~CTaskObj();
};
 
CTaskObj::CTaskObj()
{
	memset(&cliAddr, 0, sizeof(cliAddr));
	memset(&msgHeader, 0, sizeof(msgHeader));
 
	pDataBuf = NULL;
	nBufSize = 0;
}
 
CTaskObj::~CTaskObj()
{
	if (pDataBuf)
	{
		delete[] pDataBuf; pDataBuf = NULL;
	}
}
 
bool AddTaskIntoQueue(CTypedPtrArray<CPtrArray, CTaskObj*>& arrTasks, USHORT nUdpPort, USHORT nMsgID)
{
	CTaskObj* pTask = NULL;					
	try
	{
		SOCKADDR_IN addrClient;
		memset(&addrClient, 0, sizeof(addrClient));
		addrClient.sin_port = htons(nUdpPort);
 
		char pRecvBuf[1024];
		memset(pRecvBuf, 0, sizeof(pRecvBuf));
		PacketHeader* pAppHeader = (PacketHeader *)pRecvBuf;
		pAppHeader->msgid = htons(nMsgID);
 
		pTask = new CTaskObj;
		if (!pTask)
		{
			throw(-1);
		}
		memset(pTask, 0, sizeof(CTaskObj));
 
		// - copy received packet into task object
		memmove(&(pTask->cliAddr), &addrClient, sizeof(addrClient));
		memmove(&(pTask->msgHeader), pAppHeader, sizeof(PacketHeader));
 
		// no extra (optional) data are used for this task.
		pTask->pDataBuf = NULL;
 
		// - add the task into the task queue of UdpOutThread
		arrTasks.Add(pTask);
		pTask = NULL;	
	}
	catch(...)
	{
		printf("-- failed to add task into job queue. \n");
	}
 
	if (pTask)
	{
		delete pTask; pTask = NULL;
	}
 
	return true;
}
 
 
void TestTaskObjQueue()
{
	CTypedPtrArray<CPtrArray, CTaskObj*> arrTasks;
	arrTasks.SetSize(0, 10);
 
	USHORT nUdpPort = 100;
	USHORT nMsgID = 1000;
 
	AddTaskIntoQueue(arrTasks, nUdpPort, nMsgID);
	printf("--- num of items in queue = %d \n", arrTasks.GetSize());
 
	CTaskObj* pTask = arrTasks.GetAt(0);
	arrTasks.RemoveAt(0);
 
	int port = ntohs(pTask->cliAddr.sin_port);
	int mid = ntohs(pTask->msgHeader.msgid);
	printf("---data: port=%u, msgid=%u ; num of items=%d \n", port, mid, arrTasks.GetSize());
 
	if (pTask)
	{
		delete pTask; pTask = NULL;
	}
}
 
int main(int argc, char** argv)
{
 TestTaskObjQueue();
return 0;
}

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